Seismic Source Characteristics and Scaling Relations in the Northwest Himalayan Region: Case Study of Himachal Pradesh & Uttarakhand

The Himachal Pradesh and Uttarakhand areas are known for their high seismic activity in India. According to the Bureau of Indian Standards, the areas are situated in seismic zones IV and V, and have the potential to produce small to large earthquakes. These areas have also seen significant seismic events in the past. To accurately and reliably estimate the seismic hazard and simulate the characteristics of strong ground motion in the region, it is essential to evaluate the source characteristics of earthquakes and their scaling relationships. Our investigation involved the estimation of earthquake source parameters and high-frequency spectrum decay parameters using 1059 seismograms, corresponding to 247 earthquake events with magnitudes ranging from 3.0 to 5.5 that occurred in the Himachal Pradesh and Uttarakhand regions of the Northwest Himalaya between 2010 and 2020. The classic Brune’s model is used to estimate source parameters. The relationship can be expressed as \({M}_{0} = 2 \times {10}^{15}{{f}_{c}}^{-2.316}\) $M_0=2\times {10}^{15}{f_c}^{-2.316}$ for Himachal Pradesh and \({M}_{0} = 2 \times {10}^{16}{{f}_{c}}^{-3.445}\) $M_0=2\times {10}^{16}{f_c}^{-3.445}$ for Uttarakhand region, which agrees with previous studies given for the study region, providing vital insights into tectonics and structural heterogeneity beneath the respective regions of Northwest Himalaya. Our analysis revealed that for earthquakes in Himachal Pradesh, the source radius of circular fault ranges from 42 to 771 m, whereas, for events in the Uttarakhand region, it varies from 48 to 437 m. Additionally, the seismic moment ranged from 2 × 10¹¹ N-m to 9.93 × 10¹⁵ N-m for Himachal Pradesh and 1.11 × 10¹¹ N-m to 1.40 × 10¹⁶ N-m for Uttarakhand events. An increasing trend in stress drop is observed, varying from 0.0026 MPa to 8.66 MPa for Himachal Pradesh and 0.0014 MPa to 9.51 MPa for Uttarakhand, within the similar range of seismic moment. Moreover, the study highlighted that the estimation of κ and \({f}_{max}\) $f_{\mathit{max}}$ is influenced by both source characteristics and propagation path, with the source exerting a significant impact. A detailed analysis of the data suggests that the differences in how earthquakes start and fade in Himachal Pradesh and Uttarakhand are due to the complex geological structures and the intricate earthquake processes in these regions.